Innate Immune Response and Antiviral Defense Pathways

Strategic Insights -

Researchers at the University of California have identified key components of the innate immune response, including the RIG-I family helicases and IPS-1 adaptor cytosolic pathway, which play a crucial role in detecting foreign RNA and triggering the induction of type I interferon (IFN) and apoptosis. The study also found that short interfering RNAs, including T7 phage polymerase-synthesized RNA, can selectively silence gene expression and induce IFN-beta and apoptosis in certain cell lines. However, the effectiveness of this mechanism depends on the cell line and RNA length, with longer RNAs and polyinosinic-polycytidylic acid being more effective than shorter RNAs and chemically synthesized dsRNAs.

Key Takeaways:

  • The innate immune response is triggered by the recognition of foreign double-stranded RNA (dsRNA) through the RIG-I family helicases and IPS-1 adaptor cytosolic pathway.
  • The Toll-like receptor 3 and TIR domain-containing adaptor-inducing IFN-beta (TRIF) adaptor membrane-associated pathway also activates IFN regulatory factor 3 (IRF3) to produce type I interferon.
  • Short interfering RNAs, including T7 phage polymerase-synthesized RNA, can selectively silence gene expression and induce IFN-beta and apoptosis in certain cell lines.
  • The effectiveness of PRNA-mediated gene silencing and associated nonspecific pro-apoptotic and IFN-inducing effects depend on the cell line and RNA length.
  • Longer RNAs, such as 50 nucleotides, and polyinosinic-polycytidylic acid are more effective than shorter RNAs and chemically synthesized dsRNAs in activating the RNA-dependent protein kinase (PKR) and inducing significant levels of IFN-beta and apoptosis.
  • Removal of the 5'-phosphate from PRNAs decreases the induction of both IFN-beta and apoptosis.
  • Effector caspase activation and apoptosis following RNA transfection are enhanced by pretreatment with IFN.
  • PKR, IPS-1, and IRF3 are required for maximal type I IFN-beta induction and the induction of apoptosis by both transfected PRNAs and polyinosinic-polycytidylic acid.

Statistics:

  • RNA length: 50 nucleotides (effective in activating PKR and inducing IFN-beta and apoptosis) and shorter than 50 nucleotides (less effective).
  • Polyinosinic-polycytidylic acid: able to activate PKR and induce significant levels of IFN-beta and apoptosis.
  • PRNAs and polyinosinic-polycytidylic acid: both are capable of inducing apoptosis in certain cell lines.
  • PKR: required for maximal type I IFN-beta induction and the induction of apoptosis by both transfected PRNAs and polyinosinic-polycytidylic acid.
  • IRF3: required for maximal type I IFN-beta induction and the induction of apoptosis by both transfected PRNAs and polyinosinic-polycytidylic acid.

Sources:

  • Mcallister, C.S., et al. (2009). The RNA-activated Protein Kinase Enhances the Induction of Interferon-beta and Apoptosis Mediated by Cytoplasmic RNA Sensors. Journal of Biological Chemistry, 284(3), 1644-1651.
  • RNA Research (online journal).
  • University of California, Dept. of Molecular Cellular & Development Biology, Santa Barbara, CA 93106, USA.
  • American Society Biochemistry Molecular Biology Inc., 9650 Rockville Pike, Bethesda, MD 20814-3996, USA.